Equipment for monitoring physiological functions, such as the electrical activity of the heart, often outputs digital data samples at a rate that is greater than economical cathode ray tube display or other monitoring apparatus can accommodate. For example, the digital data samples may occur every two milliseconds and the display apparatus may only be capable of displaying a sample every eight milliseconds, thus requiring a four-to-one data compression. One way of providing the required compression of the data in this situation would be to average each successive group of four data samples. Unfortunately, however, this reduces the amplitude of narrow pace pulses that are of utmost importance to a point where they may become indistinguishable from noise.